Organopolysiloxanes have a very broad range of characteristics, for example, occurring as oils, rubbers, and solid resins, by virtue of variations in the composition of their basic structure, dimensions, configuration, species of pendant group, and molecular weight, among others. This, coupled with their characteristic heat resistance, cold resistance, oxidation stability, ageing resistance, releaseability, and water resistance, etc., has resulted in their use in a wide variety of industrial spheres, for example, in the textile industry, for release paper, in the electric/electronics industries, in construction, and as paint additives. However, organopolysiloxanes having the phthalic acid ester group in the molecule and a method for their preparation have both heretofore been unknown.